The objectives of the proposed work are: (1) to determine in the cat deafened as an adult, the effect of deafness on the functional effect, as measured in the adult animal, of deafness induced in the neonate on the development of the functional capabilities of the auditory system. The long-term objective of the proposed work is the understanding of auditory perception. A combination of electrical stimulation techniques and operant conditioning procedures is used in the proposed work. Permanently implanted electrodes will be placed in subcortical auditory nuclei. The animals will be required to perform detection and discrimination tasks based on electrical stimuli delivered through the implanted electrodes. The detection results will be used to further evaluate a mathematical model of threshold and to determine the effects of early and late deafness on the central auditory system. Tasks such as discrimination of laterality, sequence, and pattern will provide measures of how more complex functions of the central auditory system are affected by early and late deafness. The problems chosen for study in the proposed work were selected on the basis of the potential contribution to fundamental understanding of the hearing processes, and on the basis of the relevance to the task of transmitting auditory information via electrical stimulation of the auditory system in humans.